Field of the Invention
The present invention relates to an illumination optical system and an image projection apparatus having the illumination optical system.
Description of the Related Art
Recently, in an image projection apparatus such as a liquid crystal projector, a luminance is being improved by improving the illumination efficiency. In order to improve the illumination efficiency, it is preferred that an illumination area is narrowed and an edge portion of the illumination area is sharpened. Japanese Patent Laid-open No. 2011-90321 discloses an illumination apparatus in which an illumination plane is located at a light source side relative to a paraxial image plane of a curved image plane and also a peripheral image plane of the curved image plane is located at the light source side relative to the paraxial image plane. In this configuration, blurring of the illumination area is eased by the influence of the field curvature.
However, in the configuration of Japanese Patent Laid-open No. 2011-90321, a panel surface is set to the light source side relative to the paraxial image plane, and thus a conjugate point of the panel is located at the light source side relative to a first lens array (fly-eye lens). In this case, a high luminance part (streak) is generated at an end part of the illumination area, and therefore the effective illumination area is narrowed. As a result, it is necessary to ensure an area margin and thus the brightness is decreased. On the other hand, if the area margin is insufficient, the streak is projected and an image quality is deteriorated.